1. Field of the Invention
This invention relates to a constant speed holding apparatus for maintaining a vehicle at a constant cruising speed and, more particularly, to a constant speed holding apparatus maintaining the vehicle at a constant cruise speed through both variable speed ratio control and throttle control.
2. Description of the Prior Art
The conventional constant speed holding apparatus of this type are shown, for example, in Japanese Provisional Patent Publication Nos. 135335/1985; 39311/1983; and 29018/1983. Also, one such apparatus is described in the specification of PCT/JP87/00631, a PCT application filed by the present inventor.
A block diagram is given in FIG. 1 which illustrates the arrangement of these prior art apparatuses in a summarized form.
Referring to FIG. 1(a), the numeral 100 designates a constant speed cruise control unit, which comprises a vehicle speed detecting device 101, a vehicle speed memory device 102, a speed signal generating device 103, a cancellation signal generating device 104, a logic operation device 105, and an actuator drive device 106.
The constant speed cruise control unit 100 goes into operation as it receives an ignition signal IG from a main switch, and an actual vehicle speed value V.sub.W is inputted from a vehicle speed sensor 111 to the control unit 100, the actual vehicle speed V.sub.W being then detected by the vehicle speed detecting device 101. The detected actual speed value is outputted to the logic operation device 105, which also receives relevant data from the vehicle speed memory device 102. In the memory device 102, a preset vehicle speed or a target vehicle speed, set by the driver, is stored.
The numeral 120 designates a group of command switches which are cruise condition detecting means, i.e., switches for cruise condition setting by the driver. They include a set switch 121, a COA switch 122, an ACC switch 123, and an RES switch 124.
The set switch 121 is a command switch which stores a present vehicle speed as a set vehicle speed and controls the cruise speed of the vehicle thereafter on the basis of the stored set speed.
The COA switch 122 is a command switch for use in reducing the set vehicle speed to a level below the existing vehicle speed.
The ACC switch 123 is a command switch for use in increasing the set vehicle speed to a level above the existing vehicle speed, which performs acceleration control to provide better acceleration feeling.
The RES switch 124 is a command switch for providing an accelerated or decelerated cruise condition or a constant speed cruise condition on the basis of a previously stored set vehicle speed as a target value.
The output of each of the group of command switches 120 is sent to the speed signal generating device 103 of the constant speed cruise control unit 100.
The speed signal generating device 103, as it receives the output of each of the command switches 120, generates a corresponding desired speed signal and outputs the same to the logic operation device 105.
The numeral 130 designates a group of cancellation switches as means for detecting conditions for cancellation. The cancellation switches 130 include a clutch switch 131, a brake switch 132, and a cancel switch 133. The cancellation switches 130 are for cancelling the existing state of constant speed cruise control by the manipulation of a driver, the output of the switches 130 being sent to the cancellation signal generating device 104 of the constant speed cruise control unit 100.
It is generally known that both the cancellation switches 130 and the command switches 120 can be arranged in various ways according to the types of the vehicles in which they are mounted, but their basic roles are essentially same in all cases.
The logic operation device 105 in the constant speed cruise control unit 100 performs a specified logic operation on the basis of the outputs from the vehicle speed detecting device 101, the vehicle speed memory device 102, the speed signal generating device 103, and the cancellation signal generating device 104, to control the the actuator drive device 106, thereby to drive a throttle actuator 140. In this way, the opening of a throttle value 150 is controlled to permit constant speed cruise of the vehicle at the set vehicle speed.
A continuous variable transmission 250 includes pulleys disposed at its input and output sides and a V-belt, each of the pulleys being hydraulically variable in P.C.D (Pitch Circle Diameter) so that the transmission 250 is variable in variable-speed ratio, as shown in FIG. 1(b).
A continuous variable transmission control unit 200 consists of a regulating hydraulic pressure generating device 201, a variable speed hydraulic pressure generating device 202, and a CVT (continuous variable transmission) actuator drive device 203 as continuous variable transmission regulating means.
The continuous variable transmission control unit 200 receives outputs of various vehicle cruise information detecting devices including an input rotation angle sensor 211 and an output rotation angle sensor 212, both for detecting an actual variable speed ratio, a range position sensor 213 for drawing such cruise performance as desired by the driver, a throttle opening sensor 214 for detecting necessary throttle opening for meeting the driver's acceleration requirements, an engine-control information detecting device 220 for detecting information necessary for determining the condition of the engine, and a vehicle cruise control information detecting device 230 for detecting information necessary for vehicle cruise, and accordingly drives a regulating hydraulic pressure actuator 240 for regulating the hydraulic pressure from the output-side pulley of the continuous variable transmission correspondingly to the transmission power of the engine and a variable-speed hydraulic pressure actuator 241 for controlling the hydraulic pressure from the input-side pulley of the continuous variable transmission correspondingly to the variable speed ratio.
The manner of operation will be explained.
FIG. 2 is a flow chart showing the sequence of operations of the continuous variable transmission control unit 200 disclosed in aforesaid Japanese Provisional Patent Publication No. 135335/1985. In FIG. 2, steps S402 and S410 are not part of the prior art, but are present to facilitate a ready comparison between the present invention and the prior art. Steps S402 and S410 correspond respectively to steps S420 and S430 in FIG. 4.
In FIG. 2, a throttle opening data .theta. .sub.TH from the throttle opening sensor 214, an input-side rotation speed data N.sub.I, from the input rotation angle sensor 211, an output-side rotation speed data N.sub.O from the output rotation angle sensor 212, and a range position signal Sel from the range position sensor 213 are respectively read at step S401.
The next step S402, which is not in the prior art, is a routine for deciding whether the variable speed ratio requires compensation or not. Such compensation requirement arises when the throttle opening .theta..sub.TH is either in a non-open state or in a fully open state. When such compensation requirement occurs, processing advances to step S410.
This step S410 is a processing routine for various kinds of compensation. At step S411 included in the step S410, according to the need arising at step 402 for compensation of the variable speed ratio, a target input shaft rotation speed N.sub.IS is calculated, and at step S412 a target variable speed ratio R.sub.S is calculated on the basis of the target input shaft rotation speed N.sub.IS and the present vehicle speed. After the target variable speed ratio R.sub.S is obtained, processing advances to step S404, at which variable speed ratio control is performed as will be described hereinafter.
Otherwise, ordinary variable speed ratio control is performed at step S403, an engine characteristic routine, by calculating an engine-generated torque .tau..sub.e on the basis of the throttle opening .theta..sub.TH and the target input shaft rotation speed N.sub.IS, both read at step S401, if the decision at step S402, the routine for deciding whether the variable speed ratio requires compensation or not, is that such compensation is unnecessary. For the purpose of this calculation a map is used.
Subsequently, at step S404, a routine for regulating hydraulic pressure calculation, regulating hydraulic pressure P.sub.L is calculated which is determined by engine-generated torque .tau..sub.e and actual variable speed ratio R, and the regulating hydraulic pressure actuator 240 is operated.
Then, at step S405, a routine for variable speed hydraulic pressure calculation, a variable speed hydraulic pressure P.sub.R is calculated which corresponds to the difference between the target input shaft rotation speed N.sub.IS and the actual input shaft rotation speed N.sub.I, and the variable speed hydraulic pressure actuator 241 is driven.
In the processing routine shown in FIG. 2, it is so arranged that in case the throttle is not fully opened by reason of insufficient negative pressure reduction when the vehicle is on an uphill road during its constant speed cruise, variable speed ratio control is performed for increasing the target variable speed ratio R.sub.S so that sufficient acceleration power can be obtained.
Similarly, in case that when the vehicle on a downhill road, actual vehicle speed V.sub.W tends to exceed the predetermined vehicle speed despite the fact that the throttle is totally closed, the target variable speed ratio R.sub.S is increased through a combination of throttle control and variable speed ratio control in order to enhance engine brake performance.
In the conventional constant speed holding apparatus, however, there may be cases where speed fluctuation occurs as a result of mutual interference between constant speed control through the operation of the throttle actuator 140 and variable speed ratio control through changes in variable speed ratio during constant speed cruise of the vehicle, when there is only a slight difference between the actual vehicle speed V.sub.W and the predetermined vehicle speed. It has been impossible to prevent such speed fluctuation.